Method and apparatus for treating subcutaneous histological features

ABSTRACT

A system and method for treating subcutaneous histological features without affecting adjacent tissues adversely employs microwave energy of selected power, frequency and duration to penetrate subcutaneous tissue and heat target areas with optimum doses to permanently affect the undesirable features. The frequency chosen preferentially interacts with the target as opposed to adjacent tissue, and the microwave energy is delivered as a short pulse causing minimal discomfort and side effects. By distributing microwave energy at the skin over an area and adjusting power and frequency, different conditions, such as hirsuitism and telangiectasia, can be effectively treated.

FIELD OF THE INVENTION

This invention relates to effecting pathological changes in subcutaneoushistological features so as to eliminate unsightly or potentiallyharmful vascular and cellular conditions, without side effects and withfewer steps and less discomfort than has heretofore been possible.

BACKGROUND OF THE INVENTION

Radiation therapy is an accepted treatment for a wide variety of medicalconditions. High intensity radiant energy sources in the visible band,such as lasers, are now being widely used for both internal andextracorporeal procedures. While the microwave band, between 300 MHz and30 GHz affords the capability of penetrating deeper than visible lightwhile interacting differently with body tissue it has heretofore beenemployed primarily only in a variety of dissimilar medical procedures.

Microwave energy exerts its effect on tissue through controlled regionalheating (hyperthermia) of affected features through interaction betweenthe wave energy and magnetically polarizable tissue matter. By usingmicrowaves to establish a regional hyperthermia, it is possible topreferentially increase the temperature of diseased or unwantedhistological features to levels which are pathologically effective. Atthe same time, a necessary objective is to maintain adjacent tissue atacceptable temperatures, i.e., below the temperature at whichirreversible tissue destruction occurs. Such microwave inducedhyperthermia is well known in the field of radiology where it is used inthe treatment of individuals with cancerous tumors.

A number of specific methods for treating histological features by theapplication of microwave radiation are described in the medicalliterature. For example, a technique for treating brain tumors bymicrowave energy is disclosed in an article entitled “Resection ofMeningiomas with Implantable Microwave Coagulation” inBioelectromagnetics, 17 (1996), 85-88. In this technique, a hole isdrilled into the skull and a catheter is invasively inserted into thehole to support a coaxial radiator or antenna. Microwave energy is thenapplied to the antenna to cause the brain tumor to be heated to thepoint where the center of the tumor shows coagulative necrosis, aneffect which allows the meningioma to be removed with minimal bloodloss. Another technique in which microwave energy is utilized to treatprostate conditions is disclosed by Hascoet et al in U.S. Pat. No.5,234,004. In this technique, a microwave antenna in a urethral probeconnected to an external microwave generating device generatesmicrowaves at a frequency and power effective to heat the tissues to apredetermined temperature for a period of time sufficient to inducelocalized necrosis. In a related technique disclosed by Langberg in U.S.Pat. No. 4,945,912, microwave energy is used to effect cardiac ablationas a means of treating ventricular tachycardia. Here, a radiofrequencyheating applicator located at the distal end of a coaxial line catheterhyperthermically ablates the cardiac tissue responsible for ventriculartachycardia. As with the described methods of tumor treatment, thismethod of cardiac ablation operates by preferentially heating anddestroying a specifically targeted area of tissue while leavingsurrounding tissue intact.

While the general principle of propagating microwave energy into tissuefor some therapeutic effect is thus known, such applications are usuallybased on omnidirectional broadcasting of energy with substantial powerlevels. The potential of microwave energy for use with subcutaneousvenous conditions and skin disorders has not been addressed in similardetail, probably because of a number of conflicting requirements as toefficacy, safety, ease of administration and side effects.

As a significant number of individuals suffer from some type ofsubcutaneous but visible abnormality, therapeutic techniques whicheffectively address these conditions can be of great value. Suchfeatures which are potentially treatable by microwave energy includeconditions such as excessive hair growth, telangiectasia (spider veins)and pigmented lesions such as café-au-lait spots and port wine stains(capillary hemangiomas). Of these conditions, excessive hair growth andspider veins are by far the most common, affecting a large percentage ofthe adult population.

Unwanted hair growth may be caused by a number of factors including agenetic predisposition in the individual, endrocrinologic diseases suchas hypertrichosis and androgen-influenced hirsuitism as well as certaintypes of malignancies. Individuals suffering from facial hirsuitism canbe burdened to an extent that interferes with both social andprofessional activities and causes a great amount of distress.Consequently, methods and devices for treating unwanted hair and othersubcutaneous histological features in a manner that effects a permanentpathological change are very desirable.

Traditional treatments for excessive hair growth such as depilatorysolutions, waxing and electrolysis suffer from a number of drawbacks.Depilatory solutions are impermanent, requiring repeated applicationsthat may not be appropriate for sensitive skin. Although wax epilationis a generally safe technique, it too is impermanent and requiresrepetitive, often painful repeat treatments. In addition, wax epilationhas been reported to result in severe folliculitis, followed bypermanent keloid scars. While electrolysis satisfactorily removes hairfrom individuals with static hair growth, this method of targetingindividual hairs is both painful and time consuming. In addition, properelectrolysis techniques are demanding, requiring both accurate needleinsertion and appropriate intensities and duration. As with waxepilation, if electrolysis techniques are not performed properly,folliculitis and scarring may result.

Recently developed depilatory techniques, utilizing high intensity broadband lights, lasers or photochemical expedients, also suffer from anumber of shortcomings. In most of these procedures, the skin isilluminated with light at sufficient intensity and duration to kill thefollicles or the skin tissue feeding the hair. The impinging lighttargets the skin as well as the hair follicles, and can burn the skin,causing discomfort and the potential for scarring. Further, laser andother treatments are not necessarily permanent and may require repeatedapplications to effect a lasting depilation.

Like hair follicles, spider veins are subcutaneous features. They existas small capillary flow paths, largely lateral to the skin surface,which have been somewhat engorged by excessive pressure, producing thecharacteristic venous patterns visible at the skin surface. Apart fromthe unsightly cosmetic aspect, telangiecstasia can further have moreserious medical implications. Therefore, methods and devices fortreating spider veins and other subcutaneous histological features in amanner that effects a permanent pathological change to the appropriatetissues are highly desirable.

The classical treatment for spider veins is sclerotherapy, wherein aninjection needle is used to infuse at least a part of the vessel with asclerotic solution that causes blood coagulation, and blockage of theblood path. With time, the spider veins disappear as the blood flowfinds other capillary paths. Since there can be a multitude of spiderveins to be treated over a substantial area, this procedure istime-consuming, tedious, and often painful. It also is of uncertaineffectiveness in any given application and requires a substantial delaybefore results can be observed.

Another procedure for the treatment of shallow visible veins, which issimilar to techniques used in depilation, involves the application ofintense light energy for a brief interval. This technique exposes theskin surface and underlying tissue to concentrated wave energy, heatingthe vein structure to a level at which thermocoagulation occurs. Inparticular, these energy levels are so high that they cause discomfortto some patients, and they can also be dangerous to those in thevicinity, unless special precautions are taken. In addition, somepatients can be singed or burned, even though the exposure lasts only afraction of a second.

Due to the serious problems that the subcutaneous abnormalities cancreate in individuals, there is a general need to be able to treat suchfeatures in a manner that effects beneficial pathological change withoutadverse side effects or discomfort. An optimal therapeutic techniqueshould effect a permanent pathological change without requiring repeatedapplications to reach the desired effect. Moreover, these proceduresshould be noninvasive, should cover a substantial target area that isnot limited to a single hair follicle or spider vein, and should makeoptimum use of the energy available. Finally, pathological changesshould occur only in the targeted feature, and not in intervening orunderlying layers.

SUMMARY OF THE INVENTION

The present invention overcomes the deficiencies in previously describedmethods for treating subcutaneous features by delivering a dosage ofmicrowave energy that is maintained for only a short duration but at anenergy level and at a wavelength chosen to penetrate to the depth of achosen histological feature. The subcutaneous features are destroyed orpathologically altered in a permanent fashion by the hyperthermic effectof the wave energy while the surrounding tissue is left intact.

In accordance with the invention, the effective delivery of microwaveenergy into the subcutaneous feature can be maximized in terms of boththe percentage of energy transmitted into the body and a preferentialinteraction with the target feature itself. The microwave energy isspecifically targeted to the chosen depth and the targeted feature isheated internally to in excess of about 55° C., to a level whichthromboses blood vessels and destroys hair follicles. The ability totarget a wide area containing a number of features simultaneouslyenables a single procedure to supplant or reduce the need for repetitiveapplications.

Methods in accordance with the invention utilize certain realizationsand discoveries that have not heretofore been appreciated in relation towave energy-tissue interactions at a substantial depth (up to 5 mm belowthe skin surface). The wavelengths that are selected are preferentiallyabsorbed by a targeted feature such as a blood vessel more readily thanby skin surface and tissue. Thus, a chosen frequency, such as 14 GHz,penetrates through surface tissue to the chosen depth of the targetfeature, but not significantly beyond, and the energy heats the targetmore than adjacent tissue. Dynamic thermal characteristics are alsotaken into account, because transfer of thermal energy from small targetfeatures such as minute heated blood vessels to the surrounding tissue(the “thermal relaxation time”) is much faster than that for largervessels. The duration of a dosage, typically in the range of 100milliseconds, is varied to adjust for this size factor.

Immediately prior to, concurrently with, or after the application ofpenetrating microwave energy, the skin surface is advantageously cooled.This cooling may be effected in a number of ways such as through thedelivery, as rapidly expanding gas, of known coolants into a small spacebetween the microwave emitter and the skin surface. The use of coolantenables the surgeon not only to minimize patient discomfort andirritation, but also to adjust energy dosages in terms of intensity andduration, because heat extraction at the surface also affects heating tosome depth below the surface. The surgeon can also employ air cooling tominimize irritation while assuring results over a larger subcutaneousarea and with fewer applications.

While it is advantageous to cool the skin surface with a separate mediumin the target area immediately prior to or during wave energyapplication, it is also shown that the wave energy emitting deviceitself can be used to draw thermal energy off the skin surface. Again,the skin is heated minimally, giving the patient little, if anydiscomfort, and avoiding skin irritation. Comfort may be ensured forsensitive patients by a topical anesthetic, or by a conductive gel orother wave energy complementary substance introduced between theapplicator and the skin surface.

The energy applied is generally in excess of about 10 Joules, and theduration is typically in the range of 10 to 1,000 milliseconds, withabout 100 milliseconds being most used. The total energy delivered istypically in the range of 10-30 Joules, although the energy delivered aswell as frequency may be changed in accordance with the nature of thetargeted features, the target volume and depth. In a depilation process,for example, 10 to 20 Joules will usually suffice when a compactapplicator is used, while a higher input level, such as 20 to 30 Joules,is used for a telangiectasia treatment.

A system in accordance with the invention for use in such procedures mayemploy a tunable power generator, such as a tunable power sourceoperable in the microwave range from 2.45 GHz to 18 GHz, and means forgating or otherwise controlling the power output to provide selectedpulse durations and energy outputs. The system also can incorporatepower measurement sensors for both forward power and reflected power orcircuits for measuring impedance directly. Thereby, tuning adjustmentscan be made to minimize reflection. Power is delivered through amanipulatible line, such as a flexible waveguide or coaxial line, to asmall and conveniently positionable applicator head which serves as themicrowave launcher or emitter. The applicator head may advantageouslyinclude, in the wave launching section, a dielectric insert configuredto reduce the applicator cross-section, and to provide a better match tothe impedance of the skin surface. Furthermore, the dielectric insert ischosen so as to distribute the microwave energy with more uniformintensity across the entire cross section, thus eliminating hot spotsand covering a larger area.

If the dielectric is of a material, such as boron nitride or beryllium,oxide, which is a good thermal conductor, it can be placed in contactwith the skin and thermal energy can be conducted away from the skin asmicrowave energy is transferred. Different clinical needs can be met bymaking available a number of different dielectric element geometriesfitting within an interchangeable mount. The applicator head may furtherinclude a pressure limiting mechanism to insure that the head does notcompress vessels as the procedure is being carried out.

In addition to the range of capabilities thus afforded, the surgeon canuse ultrasound or other inspection techniques to identify the locationsof the subcutaneous features for the precise mapping of target sites.Using an indexing or aiming device or element on the applicator head,energy can be applied a minimum number of times at precise locations toencompass a maximum number of targets. Because skin and tissuecharacteristics vary, pretesting target characteristics and varying thefrequency or phase applied can increase efficiency and reduce thepossibility of side effects.

In another application in accordance with the invention, the skin targetarea may be more readily visualized by using a microwave launcherpositionable within an end unit in one of two alternate positions. Inone position, the target area can be viewed and the launcher indexed formovement into precise proximity to the target area. In yet anotherexample, a rectangular waveguide of standard size and therefore largercross-section is used, with air cooling of the skin surface. Fordepilation, a peel-off, attachable label locating a number of delineatedcontiguous target areas can be placed on the skin. When the applicatorhas been energized at each target area, the label sheet can be peeledoff, removing hair residue with it.

The applications of the process and method are not limited to conditionssuch as spider veins and unwanted hair, but further encompass pigmentedlesions and related abnormalities, as well as other temporary andpermanent skin disorders.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention may be had by reference to thefollowing specification, taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a combined block diagram and perspective view of a system inaccordance with the invention;

FIG. 2 is a side view, partially in section, of a microwave applicatorfor use in the system of FIG. 1;

FIG. 3 is a fragmentary view of the beam launching end of a microwaveapplicator in relation to a graphical representation of electric fieldstrength across the applicator;

FIG. 4 is a simplified, perspective view of a section of subcutaneousstructure, depicting different layers therein in relation to bloodvessels and hair follicles;

FIG. 5 is an enlarged sectional view of a hair structure from root toshaft;

FIG. 6 is a simplified depiction of method steps in accordance with theinvention;

FIG. 7 is a graphical depiction of loss factor curves showing thecomparative absorption of microwaves in blood and tissue at differentfrequencies;

FIG. 8 is a graphical depiction of the temperature changes at and belowthe skin surface during practice of methods in accordance with theinvention;

FIG. 9 is a graphical depiction of the variation in thermal relaxationtime for different blood vessel diameters;

FIG. 10 is a simplified perspective view of a different microwaveapplicator used in conjunction with a removable positioning sheet; and

FIG. 11 is a perspective, partially broken away, view of an alternativeapplicator head including internal cooling and a viewing system.

DETAILED DESCRIPTION OF THE INVENTION

A system in accordance with the invention; referring now to FIG. 1, isdepicted in an example intended for use in hair removal, the treatmentof spider veins and other skin disorders. This configuration includes ahand-held applicator that is suitable for potential use at any frequencywithin a suitable range, as well as for measurement of skin or tissueproperties. Such a system can be used for treating any of a variety ofskin disorders, including hirsuitism, telangiectasia, pigmented lesionsand the like. It will be apparent to those skilled in the art that wheresuch degrees of versatility and usage in different possible applicationsare not required, a simpler and less expensive system will oftensuffice. In addition, if a manually moveable applicator head is notrequired, the system can be simplified in this respect as well. In themost rudimentary example, a monofrequency unit with means for adjustingdosage driving a fixed applicator head may be adequate.

Referring to FIG. 1, in a system 10 in accordance with the inventionmicrowave energy of a selected frequency can be generated by any one ofa number of conventional devices, such as a variable frequencysynthesizer 14 that covers a range from about 2 GHz to about 20 GHz. Anumber of other conventional microwave generators are tunable in therange of 2.45 GHz to 18 GHz, for example, but here a suitablecombination includes the frequency synthesizer 14 and a traveling wavetube system 12 having internal power and a high power output amplifier.Where operating conditions are well-defined and wide tunability is notneeded, a conventional low cost source such as a magnetron may be used.The output of the traveling wave tube system 12 is gated open forselected intervals by control pulse circuits 16, which can be set, inthis example, for any interval from 10 to 1000 milliseconds. Thus, theselected frequency is delivered as a pulse burst to provide from 50 W toas much as 4 KW output, the power level most often being of the order ofa few hundred watts. In transmission to the operative site, the powerbursts are directed through a power sensor 18, which diverts bothforward and reverse propagated energy samples to a power meter 20.Readings at the power meter 20 enable the surgeon to fine tune power,phase or frequency settings to improve impedance matching and energyefficiency.

Preinspection of the target site is dependent on the nature of thetarget. Although visual inspection is sometimes alone sufficient fortarget area selection, as with hirsuitism, target veins at depth belowthe surface can often better be identified, located, and dimensioned byconventional analytical instruments, such as those using ultrasoundimaging. As is described hereafter, the power, duration and frequencyapplied can also be adjusted in relation to the thermal relaxationcharacteristics of a target blood vessel, which in turn is dependent onsize and location.

A microwave transmission line 24, here including a flexible rectangularwaveguide or a flexible coaxial section 26 that may be manuallymanipulated, supplies the microwave energy through a phase shifter orother kind of tuner 27 to a hand applicator 30 shown here as positionedagainst a limb 32 exposed within a surgical drape 34. The handpiece 30,shown in greater detail in FIGS. 2 and 3, is essentially a rectangularwaveguide device having a stepped or other impedance matching section 36coupled to the flexible coaxial line 26. The handpiece 30 includes aconverging tapered body 38 having an open aperture end 40 serving as thewave launching terminus. Internal to the tapered waveguide section 38 isa dielectric insert 44 here formed of two high dielectric (K=16) taperedstrips 46, 47 held in place between low dielectric constant (K=2.5)spacers 48 of a virtually microwave transparent material such as“Rexolite”. This configuration of dielectrics, as seen in FIG. 3,spreads the electric field distribution toward the sidewalls, enlargingthe target area that is effectively acted upon by the wave energy andeliminating any hot spot tendency within the target area. In addition,the dielectric insert 44 provides a better impedance match to the skin,reducing reflective losses, which can further be minimized byadjustments at the tuner 27. The dielectric 44 also reduces thecross-sectional area and size of the waveguide, thereby making thehandpiece 30 easier to handle. In addition, the internal taper matchesthe waveguide impedance to the different impedance of the dielectricloaded section, so as to minimize reflection.

The flexible coaxial line 26 allows a surgeon to move the applicator 30to place its open end manually wherever desired on the body surface 32.At the frequency range of 12-18 GHz, a standard WR 62 waveguide sectionwith 0.622″×0.311″ orthogonal dimensions can be employed at the outputend of the impedance matching section 36. The tapered section 38, loadedby the dielectric 44 in this example, reduces the waveguide dimension to0.250″×0.150″ at the output terminal face 40. The end face 40, however,is set off from the limb or other body surface 32 against which it isjuxtaposed by an encompassing and intervening spacer element 54, bestseen in FIGS. 2 and 3. The spacer element 54 includes an interiorshoulder 56 extending around the periphery of the end 40 of the taperedsection 38, defining a standoff volume of a height of about 0.020″ (0.5mm). A coolant can thus be injected via a side conduit 58 from apressurized coolant gas source 60 (FIG. 1), via a coupling conduit 62extending through a solenoid controlled valve 64. The pulse control 16opens the valve 64 in timed relation to the microwave pulse to bedelivered from the traveling wave tube system 12. This timing relationcan be controlled, so that the target skin area can be precooled priorto delivery of the microwave pulse, cooled concurrently with thedelivery or cooled after the start of the delivery of the microwavepulse. Furthermore, a temperature sensor 68, shown only generally inFIG. 1, may be disposed within the standoff volume, in contact with theskin or otherwise, to sense the lowering of temperature at the targetsurface. In this example, the coolant is a pressured gas, such as1,1,1,2 tetrafluoroethane, held under high pressure in liquefied orgaseous phase. When injected by actuation of the valve 64, the gasexpands vigorously within the standoff volume, rapidly lowering thetemperature because of the expansion effect. Since the boiling point ofthe tetrafluoroethane is approximately −26° C. at 1 atm, it is extremelyeffective in extracting thermal energy from the target area, even forthe short bursts of the order of a fraction of a second that areinvolved in the present procedure. The temperature sensor 68 may be aLuxtron fiber optic device for measuring temperature, or it may be athermistor which is coupled in a circuit that triggers the microwavepulse when the coolant has adequately lowered the temperature at theskin surface or in the standoff volume. Other coolants, including air,can alternatively be used to reduce the skin surface temperature withinthe standoff volume during the procedure.

Other alternative approaches may be utilized to minimize discomfort and,separately or additionally, provide improved efficiency. A compound thatis complementary to the delivery of the microwave energy, in the senseof neither being reflective or absorptive, and therefore not appreciablyheated, can be placed on the skin prior to microwave pulse application.For example, a topical anesthetic having short term effectivity may beall that is needed to reduce the discomfort of some patients to anacceptable level. Other patients may require no coolant or topicalanesthetic whatsoever. Another alternative is to employ a surface gel orother substance that improves impedance matching between the microwavepulse launching device and the surface tissues.

The microwave delivery system provided by the applicator 30 deliversmicrowave energy over an advantageously broad field distribution into asubcutaneous surface area as best understood by reference to FIG. 3. Thedielectric loading introduced by the spaced apart dielectric elements46, 47, which diverge toward the output end as the sidewalls converge inthe tapered section 38, alters the normal horizontal electric fielddistribution from its normal half sine wave characteristic so that thereis substantial field strength at the two sidewalls and no high centralenergy peak. A single, appropriately shaped, dielectric element can beused to modify the field distribution to like effect. By thus spreadingthe energy across the target area, there is both elimination oflocalized energy concentrations (and therefore localized heating) and alarger effective treatment area. As seen in the graphical portion ofFIG. 3, in the solid line, the calculated electric field at the skinsurface when the outlet end 40 of the microwave launcher is 0.5 mm offthe surface, is more than twice that at the edges. This differential isreduced when the field distribution is modeled at a depth of 0.5 mmbelow the skin surface. In both instances, there is a degree ofdispersion outside the perimeter of the applicator face 40 because ofthe setoff spacing, but this aids in equalizing the power distributionand poses no radiation danger.

In accordance with the present invention, advantage is taken of theresults of an analysis of the interaction of microwaves with biologicaltissues at different frequencies. The complex permittivity ∈* of anygiven matter, including biological matter, in a steady state field isconventionally analyzed using the following equation:∈*=∈₀(∈′−j∈″),in which ∈₀ is the dielectric constant of free space and the realcomponent, ∈′, is the dielectric constant, while the imaginarycomponent, ∈″ is the loss factor. As seen in FIG. 7, the loss factor(∈″) of blood, in the range of 2 to 20 GHz, shown by tests to besubstantially higher than that of skin tissue. Further analysis hasascertained that by considering both relative and absolute factors, themost advantageous conditions exist at about 14 GHz. From published work,the dielectric constant of skin is known to be about 22 at 10 GHz and todecrease with increasing frequency to a value of 12 at 18 GHz. The lossfactor for skin reaches a peak of 18 at 9 GHz and decreases withincreasing frequency to a value of 12 at 14 GHz. The loss factor ∈″ forskin is approximately one-half that for blood in the frequency rangebetween 14 GHz and 20 GHz, and above 10 GHz the loss factor for bloodincreases somewhat more than for skin, as seen in FIG. 7. Therefore, theheat generated per unit volume in blood and to some extent indifferentiable cellular structures other than skin, can be expected tobe twice that of skin. Consequently, differential heating results whenmicrowave energy penetrates subcutaneous regions. Because thesesubcutaneous regions are of depths up to 5 mm, they are directly withinthe range of interest that includes hair follicles and roots,telangiectasia, pigmented lesions, and other histological features thatare visible through the epidermis and/or dermis, or actually protrude atthe skin.

The structure of skin is somewhat idealistically and simplisticallydepicted in FIG. 4, in order to show the physical relation and relativeproportions (although not to scale) between the epidermis and dermislayers that lie above subcutaneous tissue, and to further representhistological features of interest in the structure. Sweat glands, nerveendings, corpuscular structures and sebaceous glands are not includedfor clarity. The hair shafts, most deeply embedded at their roots at 4to 5 mm depth in the dermis, extend outwardly through the dermis and therelatively more robust epidermal layer. Relatively large arteries andveins branch into the arteriole and venule vessels which feed and deriveblood, respectively, as the smallest capillaries that normally areinvisible from the skin surface, and that form the termini of the bloodpaths. When these capillaries, either or both arterioles and venules,become engorged for some reason, as in the telangiectasia condition,they form the lateral and visible pattern, known collectively as spiderveins, at a depth of 0.1 to 1.0 mm below the surface of the epidermis.Typically of the order of 0.2 mm in diameter, the spider veins canactually sometimes protrude at the surface, and be larger in diameter aswell. Reticular or feeder veins can lie as much as 5 mm in depth belowthe surface, and are substantially larger, of the order of 1.0 to 2.0 mmin diameter, being large enough to be identified by a non-invasiveinspection technique, such as imaging with ultrasound. The reticular orfeeder veins sometimes create the overpressure condition causingengorgement of the spider veins.

FIG. 5 shows further details, again somewhat idealized, of an enlargedhair shaft, extending outwardly from a root into the growing cellularstructure of the follicle and the follicle casing that transforms intothe hair shaft body that passes through the epidermis. The hair follicleis nourished by at least one artery that feeds the papillae structure atthe root and is encompassed in a crown of associated matrix cells.Attack on the cellular follicle structure or on the papillae or thearterioles or venules to and from the papillae can result in permanentdestruction of the hair shaft.

With these considerations in mind, appreciation of the operation of thesystem of FIG. 1 can more readily be gained. The surgeon can use asuitable frequency for a chosen histological feature within the range ofthe frequency synthesizer 14. It is assumed here that the frequencychosen is about 14 GHz. The traveling wave tube system 12 is set togenerate approximately 100 to 300 watts, the control pulse circuits 16being set to open the solenoid valve 64 prior to getting a short pulsefrom the microwave system 12. It has been found that a 100 millisecondpulse is satisfactory for both efficacy and safety, although otherdurations can be used with wattage adjustments to compensate. The outputfrom the traveling wave tube system 12 is directed through the powersensor 18, the transmission line 24, the flexible section 26, throughthe tuner 27 and to the applicator 30. If the operator desires, shorttest pulses of low amplitude can first be sent to obtain readings of thereflected power at the power meter 20, and fine tuning adjustments canbe made at the tuner 27, in a conventional manner. In addition, theoperator can use ultraound or another non-invasive diagnostic system toanalyze the substructure to identify the position of target features,such as reticular veins and arteries, both as to size and location. Theprocedure initially to be described, however, pertains to depilation, sothat the target area is not only readily visible, but is alsosubstantially uniform in depth and structure, as per FIG. 5.

When the control pulse circuits 16 operate, they first provide a controlimpulse to open the solenoid valve 64, in this example, and then turn onthe traveling wave tube system 12 for the selected interval. Because thevalve requires a few milliseconds (e.g., 20 to 35) to operate and a fewmilliseconds are also needed for the pressurized coolant from the source60 to pass through the outer conduit 62 and the side conduit 58 in thespacer 54, it is preferred to delay the microwave pulse until coolinghas actually begun or is contemporaneously begun. Alternatively, aspreviously noted, a temperature sensor 68 that detects a temperaturedrop at the skin surface may be used to either trigger the microwavepulse or to preclude its operation until after the coolant has becomeeffective.

For depilation, pulses in the range of 10 to 20 Joules in terms of totalwork output have been shown to effect permanent depilation withoutsignificant discomfort or significant adverse side effects. Tests wererun using the dielectric loaded applicator 30 having a 0.250″×0.150″output area (5 mm×3 mm, or 15 mm²), and employing a pulse duration of100 milliseconds in all instances. A substantial number of experimentswere run on test rabbits with this applicator, varying only the powerapplied so as to change the total energy in Joules. The results wereexamined by a pathologist and the accompanying Tables 1 and 2, appendedfollowing the specification, show the results of his examination.

The system of FIG. 1 was also employed in a number of tests on rabbitsto determine the changes occurring in veins and arteries under differentpathological changes, and side effects on tissues and vessels with aprotocol using cooling as well as no cooling to determine ifpigmentation has an effect are shown in appended Table 3. These testsshowed no significant difference in pigmentation versusnon-pigmentation; indicating that coloration, and/or the presence ofmelanin, is not a significant factor in absorption of microwave energy.A different protocol was followed in amassing results shown in appendedTable 4, which represents an analysis by a pathologist blinded to thedosages used. Cooling was not used in this example. These results withtest rabbits show that pigmentation is not a significant factor and thatat 16 Joules dosage and above, there is effective occlusion of targetveins and arteries with minimal changes or only mild induration oftissues. The indication of dermal fibrosis again is not indicative ofscar development.

Pathological examination of these animal studies consistentlydemonstrated destruction of hair follicles over a wide range ofmicrowave energy levels. The destruction extended to the base of thefollicle, which is significant to permanent hair removal. The amount ofhair destruction within the target area varies in accordance with thetotal amount of energy, but destruction is substantially complete at 14Joules and higher. Furthermore, until the energy delivered is in excessof 20 Joules, the appearance of the skin is normal in all cases and theepidermis is histologically intact. Minor indications of dermal fibrosisare not indicative of clinical scar formation. Minor vascular changes,such as intimal fibrosis of small arteries, constitute neither damagingnor permanent conditions. Consequently, a dosage in the range of 14 to20 Joules is found both to be effective and to be free of deleteriousside effects.

The effects of delivery of microwave energy, with surface cooling, areillustrated graphically in FIG. 8, which indicates temperature changesat both the surface of animal skin tissue (0.75 mm thick) and 1.5 mmbelow the surface, in water, under conditions of delivery of up to 12Joules total energy level over 100 milliseconds duration, accompanied bycooling using expanded tetrafluorethane gas. As shown, the baselinetemperature for the test animal skin is approximately 32° C., and thatfor the body at a depth of 1.5 mm is approximately 37° C. Applying themicrowave energy with cooling, the skin surface temperature rose veryslightly, but was essentially unchanged. Beneath the skin surface,however, the temperature rise at 1.5 mm depth was at a substantiallyhigher rate, reaching approximately 60° C. at 100 milliseconds. Highertemperatures would of course be reached with the application of higherenergy levels. It is posited that even such a temperature is sufficientto cause cellular degradation of the hair follicles near the root, andit may well also thermocoagulate blood in the feeder artery, in thepapillae at the hair root, or in the cell matrix surrounding thepapillae. Although the hair follicles are not conductive, they may beparticularly susceptible to the impinging microwave energy because theyare thin dielectric elements which can cause energy concentration andtherefore greater heating. Whether one or more effects are observable,permanent destruction has been shown by pathological examination, as inthe annexed tables.

The microwave energy does not significantly penetrate beyond the depthof the targeted histological features because of attenuation, thelimitation on total energy delivered and the lower loss factor intissue.

Where the histological defects are benign vascular lesions, as with thetelangiectasia condition, different tests and operating conditions maybe employed, as shown in the steps of FIG. 6, to which reference is nowmade. While spider veins can cover a substantial area, and visualtargeting may be sufficient, it is often desirable to analyze the targetarea in greater detail. Thus, ultrasound examination may be utilized toidentify and estimate the size of reticular veins feeding a substantialarea of spider veins, as an optional first step 80, which can precedemarking of the target surface 82 in any appropriate way. Again, thedielectric constant, skin impedance or other characteristics may betested in a preliminary step 84, prior to choosing operative frequencyin step 86. Fine tuning, phase adjustment or another impedance matchingoption 88 may be employed to reduce reflective losses and increaseefficiency. Given the size and location of the target vascular feature,thereafter, the power level and pulse duration may be selected in a step90.

The pulse duration is a significant parameter in relation to the vesseldiameter, since the smaller the vessel diameter, the shorter is thethermal relaxation time. Even though the loss factor of blood is higherthan that of the tissue, dissipation of heat to surrounding tissue ismuch faster with a small blood vessel and consequently shorter termheating is needed. As seen in FIG. 9, thermal relaxation time increasesmonotonically with vessel diameter, and thus a longer duration pulse isneeded, perhaps at the same or a greater power, if the vessel diameteris of a larger size. Given the power level and pulse duration, theoperator can select one of the cooling options, which also includes nocooling whatsoever, in step 92. Typical anesthetics or other anestheticsmay be employed at the same time, as shown by optional step 94.

Consequently, when the microwave pulse is delivered, the subcutaneoustarget is heated to the range of 55° C. to 70° C., sufficient tothrombose the vascular structure and terminate flow permanently. Thespecific nature contributing factors to disappearance of the vesselswith time may be one or more factors, including thermocoagulation of theblood itself, heating of the blood to a level which causes thrombosis ofthe vessel or some other effect. The net result, however, is that afibrous structure forms in the vessel which clogs and terminates flow,so that the resultant fibrous structure is reabsorbed with time, as newcapillary flow paths are found. In any event, heating in the 55° C. to70° C. is sufficient to effect (step 96) the permanent pathologicalchange that is desired (step 98).

An alternative applicator that covers a larger area and is employed witha peelable indicia label as shown in FIG. 10. The standard WR 62waveguide for transmission of microwave energy at 14 GHz has, aspreviously mentioned, interior dimensions of 0.622″×0.311″. Anapplicator. 100 employing such a waveguide section 101 is used directly,without internal dielectric loading, to cover a substantially largertarget area while employing air cooling. The waveguide section 101,coupled via a flexible waveguide and an impedance matching transition(not shown), if necessary, to a microwave feed system 102 has side wallports 104 coupled to an external coolant source 105 which may delivercoolant through a control device 106 triggered, in relation to themicrowave pulse, as previously described. Under some circumstances, whenair is used as the coolant, it may simply be delivered continuously intothe waveguide, the end of which can be blocked off by a microwavetransmission window so that only the launching end and the skin surfaceare cooled. For use in a depilation procedure, the skin surface of apatient to be treated is covered with a sheet 108 having numbered guideindicia 109 for marking successive applicator 100 positions. Thesepositions overlap because of the fact that the energy concentration isin the central region of the waveguide 101, at the normal maximumamplitude of the electric field in the TE₁₀ mode. The peel off labelsheet 108 is covered on its skin-adhering side by a separable adhesive.Consequently, when the applicator 100 is moved between successiveoverlapping index positions marked 1,1,2,2 etc. at the side and cornerof each position, the internal areas that are pathologically affectedwithin each location are essentially contiguous, until the entireapplicator 100 has been moved through all positions on the sheet 108,with dosages applied to all of the areas. Hair follicles having beendestroyed in those areas, the procedure is terminated and the sheet 108is peeled off, with the destroyed hair follicles and shafts adhering toit.

With the arrangement of FIG. 10, a longer microwave pulse duration ormore wattage is needed for increasing the number of Joules because ofthe broader beam distribution, which means that, heating is at a slowerrate (e.g., in the approximate proportion of 0.7° C. rise in skintemperature per joule for the large applicator versus 2.4° C. per joulefor the dielectric filled smaller applicator). The skin temperature risewas reduced by a factor of 2 when using air at a temperature of between0° C. and −5° C.

It should be noted, furthermore, that a standard open rectangularwaveguide can be loaded with dielectric elements in a manner whichenables size to be reduced without restricting coolant flow.

Another alternative that may be used, but is not shown in the figures,relates to a modification of the spacer element that is employed in theexample of FIGS. 2 and 3. One can configure the spacer element with twoalternative but adjacent positions for the applicator open (emitter)end, and arrange the applicator so that the emitter end can be shiftedbetween the two positions. In a first or reserve position of theapplicator, the target surface can be viewed through the spacer element,and positional adjustments can be made. This part of the spacer elementis then used as a frame for visualizing the operative target on the skinsurface when the applicator is in the reserve position. As soon as thetarget area is properly framed, the applicator is simply shifted fromthe reserve position to the operative position, in proper alignment withthe target area, and the procedure can begin.

A different approach to a useful applicator is shown in FIG. 11, towhich reference is now made. This also illustrates a different means forcooling the skin surface, as well as for viewing the target area. Inthis example, the applicator 120 comprises an open-ended wavepropagation segment 122 fed via a transition section 124 from a coaxialline 126. The unit may be physically manipulated by an attached handle128. The open end of the waveguide 122 is filled by a dielectric element130 which is not only of suitable electrical dielectric properties but agood heat conductor as well, such as boron nitride or beryllium oxide.The dielectric insert 130 extends beyond the open end of the waveguide,into contact with a skin surface that is to be exposed to microwaveradiation. The interior end of the dielectric 130 is urged in thedirection toward the skin surface by a non-conductive, non-absorptivemicrowave leaf spring 134 of selected force and compliance. Thus, thedielectric insert 130 presses on the skin surface with a yieldableforce, selected to assure that contact is maintained but that anyprotruding veins or arteries are not closed simply by the force of theapplicator 120. This applicator 120 and dielectric insert 130 areexternally cooled by an encompassing sleeve 136 through which coolant ispassed via internal conduits 137, 138 that communicate with an externalsupply (not shown) via external conduits 141, 142. Consequently, heat isextracted from the surface of the skin via the contacting dielectric 130itself.

In addition, a target mark placed on the skin surface by the surgeon maybe viewed by a system including a fiber optic line 145 that extendsthrough the dielectric 130 and leads via a flexible fiber optic line 147to an image viewing system 149.

In use, this applicator 120 of FIG. 11 covers a substantial chosen area,with the viewing and cooling features that simplify placement andminimize discomfort. The movable dielectric insert 130 can be areplaceable element, with different shapes of dielectrics beingsubmitted where different conditions apply. It will be appreciated thatother expedients may be utilized for shaping the microwave beam,including lens and diffuser systems.

Although a number of forms and modifications in accordance with theinvention have been described, it will be appreciated that the inventionis not limited thereto, but encompasses all forms and expedients inaccordance with the appended claims.

TABLE 1 ANIMAL STUDY PROTOCOL NP970305 Applicator Tip: 0.250″ × 0.150″;Cooling Dose Description Histologic Description Rabbit (Joules) of SkinTissue Hair Follicles Vasculature B9  13 skin intact; some few hairvessels decreased fibrosis; follicles patent density of mild edema hairB10 15.2 skin intact; dermal relative vessels decreased fibrosis absencepatent density of of hair hair follicles B11 19.6 skin intact; normalpaucity vessels decreased of hair patent density of follicles hair

TABLE 2 ANIMAL STUDY PROTOCOL NP970505 Applicator Tip: 0.250″ × 0.150″;Cooling Dose Description Histologic Description Rabbit (Joules) of SkinTissue Hair Follicles Vasculature B1/R 22.4 skin intact; tissue absent,veins patent; hairless viable, squamous arteries dermal metaplasiapatent; fibrosis increased intimal fibroblasts B1/L 22.4 skin intact;tissue hair follicle veins patent, hairless viable, destruction arteriesdermal patent, fibrosis intimal fibrosis B2/R 20.0 skin shiny; tissuehair follicle possible hairless viable, destruction fibrous cord dermalin small vein; fibrosis arteries not seen in these sections B2/L 20.0skin intact, tissue hair follicle veins patent; shiny and viable,destruction arteries hairless dermal patent, fibrosis increased intimalfibroblasts, mild edema B3/R 24.1 skin shiny tissue hair follicle veinspatent; and viable, destruction; arteries not hairless, dermal squamousseen in these fine fibrosis, metaplasia sections granularity small areaof necrosis on opposite side of ear (no cooling) B3/L 23.6 threesubacute absence of hair vessels not indurated granulation folliclesseen in these areas, tissue sections crusting of epidermis, hairlesssingle punched out area B4/R 23.7 skin shiny tissue absence of hairfibrous cord and viable, follicles in small vein; hairless; dermalarteries not fine fibrosis seen in these granularity sections B4/L 23.6four tissue hair follicle congestion of indurated viable, destructionsmall caliber areas dermal veins; intimal fibrosis fibrosis, narrowingof small arteries B5/R 20.7 skin intact; tissue absence of hair veinpossibly hairless viable, follicles, narrowed; dermal squamous arteriesfibrosis metaplasia patent, intimal fibrosis B5/L 21.4 skin intact,tissue absence of hair veins patent; hairless, viable, folliclesarteries tiny hole dermal patent, fibrosis intimal fibrosis B6/R 22.0skin intact, tissue absence of hair veins patent; hairless, viable,follicles, narrowed fine dermal squamous small artery granularityfibrosis metaplasia with intimal fibrosis B6/L 22.0 punched dermal hairfollicle arteries and out area fibrosis destruction, veins patentsquamous metaplasia B7/R 19.2 skin intact, minimally focal area of hairveins patent; hairless affected follicle partial destruction thromboisof small artery B7/L 20.5 skin intact, dermal focal paucity of veinspatent; hairless fibrosis hair follicles, arteries squamous patent,metaplasia minimal intimal fibrosis B8/R 19.0 skin intact, focal areasfocal destruction veins patent; hairless of dermal of hair folliclesocclusion of fibrosis small artery with fibrous cord B8/L 21.4 skinintact, dermal destruction of veins patent; hairless fibrosis, hairfollicles arteries not small zone seen in these of nodular sectionsfibrosis B9/R 23.0 skin intact, small zone relative absence veinspatent; hairless of dermal of hair follicles, arteries patent fibrosissquamous metaplasia B9/L 23.0 skin intact, dermal destruction of veinspatent; hairless fibrosis hair follicles, arteries patent squamous withmild metaplasia intimal fibrosis B10/R 24.6 skin intact, milddestruction of veins patent; hairless fibrosis hair follicles arteriespatent with mild intimal fibrosis B10/L 24.7 skin intact, dermaldestruction of veins patent; hairless fibrosis hair follicles partialthrombosis of small artery B11/R 22.4 skin intact, minimal minimalchanges veins patent; hairless changes arteries patent B11/L 21.5 skinintact, dermal destruction of veins patent; hairless fibrosis hairfollicles, arteries patent squamous metaplasia B12/R 20.6 skin intact,dermal destruction of veins patent; hairless fibrosis hair follicles,arteries patent squamous metaplasia, remnants of follicles seen B12/L19.6 skin intact, zone of destruction of veins patent; hairless dermalhair follicles arteries patent fibrosis

TABLE 3 ANIMAL STUDY PROTOCOL NP970603 Applicator Tip: 0.250″ × 0.150″Dose Rabbit Pigmented (Joules) Cooling Appearance of Skin A1 No 5.3 Noskin intact - back and ear Yes skin intact - back and ear A2 Yes 5.6 Noskin intact - back and ear Yes skin intact - back; tiny dot left ear B1No 9.4 No back - minimal pallor 2/3 sites; skin on ear intact Yes skinintact - back and ears B2 Yes 9.3 No skin on back obscured by hairgrowth; skin on ear intact Yes skin on back obscured by hair growth;skin on ear intact C1 No 14.3 No back - slight abrasion 2/3 sites, smallscab 3; skin on ear intact Yes skin intact - back and ear C2 Yes 14.8 Noskin on back obscured by hair growth; skin on ear intact Yes skin onback obscured by hair growth; skin on ear intact D1 No 18.4 No back -scabs all 3 sites; ear - tiny scab Yes back - slight pallor 2/3 sites,minimal change at site 3; ear - minimal change D2 Yes 18.6 No back -small, raised areas at all 3 sites; ear - small raised area Yes skinintact - back and ear

TABLE 4 ANIMAL STUDY PROTOCOL NP970208 No Cooling Histology- Histology-Histology- Clinical- Clinical- Rabbit Joules Tissue Vein Artery TissueVessels D1/R 10.4 Viable, Patent Narrowed Intact Vein sl. dermal Purplefibrosis D1/L 10.4 Viable, Partial >occlusion Intact Narrowing dermalocclusion than vein edema D2/R 10.4 Viable, Sl. altered, Sl. altered,Small area Patent, sl. dermal but patent but patent of darkeningfibrosis blanching D2/L 10.4 Viable, Patent Tiny, vessel Small areaPatent, sl. dermal collapsed of darkening fibrosis blanching C1/R 12.0Viable, Micro- Patent Sl. Vein seg- dermal thrombosis blanching mentallyfibrosis narrowed C1/L 12.0 Viable, Ghosted, Narrowed Sl. Vein dermalwithout and focally blanching narrowed fibrosis endo- thrombosedsegmentally thelium, but patent. Venular congestion C2/R 12.0 Viable,Organiza- Not Mild Vein dermal tion with described blanching narrowedfibrosis evidence of seg- recanali- mentally zation C2/L 11.6 Viable,Thrombosis Not Mild Vein dermal with described blanching narrowedfibrosis organization seg- mentally B1/R 14.0 Viable, Patent; not Notwell Mild Vessel seen dermal well seen in visualized blanching fibrosisareas of fibrosis B1/L 13.7 Viable, Ghosted, Patent Mild Vessel seendermal necrotic, blanching fibrosis contains blood B2/R 14.0 Viable,Patent Lumina Mild Vessel seen dermal narrowed by blanching fibrosisintimal hyperplasia B2/L 13.6 Viable, Occlusion Not Minimal Vein dermalfocally described changes narrowed fibrosis seg- mentally A7/R 16.0Viable, Focally Focally Minimal Mild dermal occluded occluded changesblushing fibrosis around vein A7/L 16.3 Viable, Partial >occlusion MildBlushing dermal occlusion, than vein induration around fibrosiscongestion vein of venules A6/R 15.5 Viable, Patent Focal Minimal Veinsseen dermal occlusion changes fibrosis A6/L 15.5 Viable, Focally FocallyMild Vein seg- dermal absent absent blanching mentally fibrosis narrowedA5/R 17.4 Viable, Thrombosis Thrombosis Mild Vein dermal with withblanching narrowed fibrosis organization organization A5/L 17.5 Viable,Occlusion Not Mild to Vein scale crust (organ- described moderatenarrowed present, zation) induration dermal fibrosis

1. A method of treating a targeted subcutaneous histological featurebelow a skin surface in the human body with microwave energy, the methodcomprising the steps of: selecting a microwave frequency in which theloss factor of the targeted subcutaneous histological feature is greaterthan the loss factor of tissue surrounding the targeted subcutaneoushistological feature; and directing microwave energy at the selectedfrequency into the skin with a power density and for a durationsufficient to raise the temperature of the targeted feature to a levelwhich results in a permanent change in the pathology of the targetedfeature due to interaction of the electric field of the microwaves withthe targeted feature.
 2. The method as set forth in claim 1 above,including the step of spreading the microwave energy with a distributedenergy throughout an area at the depth range of the targetedsubcutaneous histological feature.
 3. The method as set forth in claim 2above, including the further step of cooling tissue between the skinsurface and the targeted subcutaneous histological feature during atleast a portion of the treatment.
 4. The method as set forth in claim 1above, wherein the targeted subcutaneous histological feature compriseshair and the interaction of the electrical field of the microwaves withthe hair induces heating of the hair to cause permanent destruction ofthe follicles.
 5. The method as set forth in claim 4 above, wherein thetargeted subcutaneous histological feature comprises hair rootsapproximately 5 mm below the skin surface, and wherein the methodfurther includes the step of controlling power density and duration ofthe microwave energy to radiate the targeted subcutaneous histologicalfeature with 10 to 15 Joules of energy.
 6. The method as set forth inclaim 1 above, wherein the targeted subcutaneous histological featurecomprises blood vessels of about 0.1 mm diameter or greater and located2 mm or less below the skin surface, and wherein the microwave energythromboses blood in the blood vessels by raising blood temperature to inexcess of 55° C.
 7. The method as set forth in claim 6 above, wherein,the microwave frequency is in a range of 10-20 GHz, the microwave energyis in a range of 20 to 30 Joules, and the duration is shorter than atime for thermal relaxation of blood vessels in the targetedsubcutaneous histological feature.